Victoria Azarenka successfully defended her Australian Open title to retain the world No. 1 ranking with victory over Li Na.

The Belarusian lost the opening set, but bounced back to claim a dramatic 4-6 6-4 6-3 victory at Melbourne Park.

Azarenka, who was accused of gamesmanship for a controversial injury timeout during her semi-final win over Sloane Stephens, had to wait on her opponent this time as Li twice took a medical timeout - once for an ankle problem and the second time for a head injury after an awkward fall when her ankle appeared to give way.

But the top seed showed real strength of character to remain focused and survived a determined effort from Li to claim her second career grand slam title.

Azarenka had won her last four encounters against Li, but had never beaten the Chinese No. 1 at a major with defeat at both the Australian Open and French Open in 2011, when Li went on to reach the final at both tournaments.

Serving failures was the theme of the opening set, which featured seven breaks of serve and saw Azarenka gift her opponent the set with a double fault.

It was a set bookended by poor serves, as Li, showing signs of nerves, opened with a double fault before gifting the opening game to her opponent. However, she hit straight back, and took control of the opening set when Azarenka failed to hold her serve for a third time.

The Belarusian showed real grit to break back with Li serving for the set, but after saving three set points on serve, handed her opponent the opening set with a double fault, prompting cheers from a pro-Li crowd.

But Azarenka had begun to find her rhythm, forcing Li deep behind the baseline, and grabbed an early break before her first ace of the match saw her move ahead in the second set, but a double break was swiftly negated after a couple of sloppy errors.

With Azarenka a break up, Li took a tumble after turning her left ankle when trying to change direction at the baseline. Signalling for the trainer, she limped gingerly back to her chair, and after a brief delay returned to court with her ankle heavily strapped.

Any concerns over the former French Open champion's mobility were swiftly eased as she held serve before forging three break points as the timeout appeared to have rattled Azarenka.

But in what proved to be a pivotal moment in the match, Azarenka saved all three - the first with a lovely cross-court backhand winner, hammering away a forehand winner after a net cord for the second and she was grateful to see the third thrown away by Li, who dumped a backhand into net with the court at her mercy.

Azarenka saw two break points of her own pass her by and she was broken back, but she dug deep and broke once again to wrap up the second set and force a decider.

For the third successive time, Li failed to hold her serve at the start of the set as Azarenka took first blood in the decider, only to inexplicably lose her subsequent service game as the momentum swung back in Li's favour.

Play was paused for a second time for a fireworks display to celebrate Australia Day, but on the first point after resuming, Li's ankle buckled once again and she fell awkwardly, hitting her head as she fell.

After a second medical timeout, Li returned, and with her mobility affected began going for her shots in an attempt to hit clean winners. Although she had some success, Azarenka broke for a 3-2 lead, and held her nerve to see out the victory to become only the fifth active women's player to boast multiple major titles.